Annunciator circuit



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M/ 0 5 9 1 4 2 P a |1/ JI O mKSQu Patented Oct. 24, 1950 ANNUNCIATORoIRcUl'r Paul E. Demers, Montreal, Quebec, Canada, as-

signor, by mesne assignments, to Northern Electric Company,Limited,'Montreal, Quebe Canada, a corporation of Canada ApplicationMarch 1.1, 1947., Serial No. 733,871

This invention relates to annunciator circuits and more particularly toathermistor controlled annunciator circuit.

An object of this invention is to provide anew and eicient electricalcontrol circuit.

In one embodiment of this invention an annunciator circuit is controlledwith the aid of a type of varistor known as a thermistor which is asemi-conductor having a relatively large negative coefficient ofresistivity that provides a relatively largedecrease in resistance for asmall increase in temperature. The negative resistance characteristicsof a thermistor are utilized in a normally high resistive circuit tomaintain an operating voltage to an annunciating device bythe loweringof the thermistor resistance due to the.: current increase after themomentary actuationv of a switch to momentarily remove a shuntresistance connected across the annunciating device.

The circuit contemplated in a specific embodiment of the invention isemployed to actuate and maintain in operation an annunciating device,for example a neon lamp, by the momentary opening of a normally closedswitch until another switch is momentarily opened whereupon theannunciating device is deenergized.

A complete understanding of the invention will be had by reference tothe following detailed description taken in conjunction with thesingle-figure drawingwhich is a circuit diagram of a preferredembodiment of the invention.

As shown in the drawing a neon lamp I and a series-connected resistor IIare connected to a suitable voltage supply I2 through a thermistor I3and a normally closed switch I4; and a resistor I5 is normally shuntedacross the lamp I0 and the resistor II through a normally closed switchI6. The values and characteristics of the various circuit elementsshould be such that with the switches in their normal or closed positionthe voltage across the annuncia-ting device which may be the neon lampI0 will be below the striking or firing voltage oi the lamp. Thethermistor I3 under these conditions may have a resistance of about100,000 ohms, but in any event the resistance should be high enough tokeep the voltage across the lamp below its striking or firing voltagewhen the circuit is quiescent; and the resistor I 5 should have aresistance such that the voltage drop across it is below the voltagenecessary to re the neon lamp and suiilciently high so that the currentthrough the thermistor will be below any value that would appreciablylower its resistance while the circuit is in the unoperated condition.

3 Claims. (Cl. 315-289) It has been found that a resistance value of800,000 ohms for the resistor I5 inthe circuit shown will operatesatisfactorily. The resistor II may be 14,000 ohms and serves to limitthe current through the lamp IU when it is red.

In the operation of the circuit, momentary opening of switch I6 willapply suiiicient voltage to the neon lamp I0 to cause it to fire andglow. This increases the current flow through the thermistor, and,because of its negative-resistance characteristic, the resistance of thethermistor will then change from 100,000 ohms to about 2,000 ohms, thuslowering the resistance ofthe supply circuit, which, together with thefact that a relatively low maintaining voltage is required by the neonlamp will maintain the glow l of the lamp. The lamp I0 will continue toglow even though the resistor I5 is again shunted across both the lampand the resistor II by the immediate closing of switch I6 after havingbeen momentarily opened to re the lamp. However, the lamp may beextinguished by disconnecting the supply circuit from the lamp bymomentarily opening switch I4, the subsequent closure of which preparesthe circuit for another cycle of operation when required. Obviously,either the switch I4 or the switch I6 may be remotely controlled inorder to operate the lamp from a distance as an annunciating device.

Although the circuit described herein utilizes a thermistor any devicehaving similar negative resistance characteristics may be substitutedfor the thermistor in the circuit.

The circuit described herein may be used to operate or control devicesother than neon lamps especially devices having an initiating voltagehigher than the maintaining voltage. Such a device would simply besubstituted for the neon lamp in the circuit.

What is claimed is:

1. An electrical signalling system comprising, an ionizable gas filledtube operable in response to a predetermined voltage thereacross and,unless operated, presenting a substantially open circuit to voltagesbelow said predetermined voltage, a resistor connected in parallel withsaid tube, a voltage source, a thermistor connected in. series with saidparallel connected resistor and tube across said source, the value ofsaid resistor being such that the voltage thereacross is below saidpredetermined voltage value and the current therethrough is insufficientto appreciably lower the resistance of said thermistor before operationof said tube, and means to momentarily remove said resistor from thecircuit and thereby increase the voltage across said tube to a Valueequal to or above said predetermined voltage value, said increase beingof such proportions that the current now resulting therefrom reduces theresistance of said thermistor to a value such that reconnection of saidresistor across said tube after operation thereof does not aifect saidoperation.

2. An annunciator circuit comprising an ionizable gas filled tubeoperable in response to a predetermined voltage thereacross and, unlessopl erated, presenting a substantially open circuit to voltages belowsaid predetermined voltage, a resistance element connected in parallelwith said tube, a voltage source, a negative coefcient resistorconnected in series with said parallel connected resistance element andtube across said source, the value of said resistance element being suchthat the voltage thereacross is below said predetermined voltage valueand the current therethrough is insufcient to appreciably lower theresistance of said negative coefficient. resistor before operation ofsaid tube, means to momentarily remove said resistance element from thecircuit and thereby increase the voltage across said tube to a valueequal to or above said predetermined voltage value, said increase beingof such proportions that the current ow resulting therefrom reduces theresistance of said negative coefficient resistor to a value such thatreconnection of said resistance element across said tube after operationthereof does not affect said operation, and means to disconnect saidkvoltage source from the circuit,

3. An electrical signalling system comprising an ionizable gas filledtube operable in response to a predetermined voltage thereacrcss and,unless operated, presenting a substantially open circuit to voltagesbelow said predetermined voltage, a resistor connected in parallel withsaid tube, a voltage source, a thermistor connected in series with saidparallel connected resistor and tube across said source, the value ofsaid resistor being such that the voltage thereacross is below saidpredetermined voltage value and the current therethrough is insufficientto appreciably lower the resistance of said thermistor before operationof said tube, means to momentarily remove said resistor from the circuitand thereby increase the voltage across said tube to a value equal to orabove said predetermined voltage value, said increase being of suchproportions that the current flow resulting therefrom reduces theresistance of said thermistor to a value such that reconnection of saidresistor across said tube after operation thereof does not affect saidoperation, and means for disconnecting the voltage source from thesystem.

PAUL E. DEMERS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,215,123 Kalischer Sept. 17,1940 FOREIGN PATENTS Number Country Date 587,660 Great Britain May l,1947 OTHER REFERENCES K Becker et al.: Properties and Uses ofThermistors, Trans. of American Institute of Electrical Engrs.,Electrical Engineering Transaction Section, Nov. 1946, pp. 711 to 725.

